Effect of small molecular surfactants on physical, turbidimetric, and rheological properties of Pickering nanoemulsions stabilized with whey protein isolate

In the present study, Pickering nanoemulsions (oil-in-water) co-stabilized with whey protein isolate (WPI) and three types of small molecular surfactants were prepared. Hexadecyltrimethylammonium (CTAB), sodium dodecyl sulfate (SDS), and Tween 20 were used as cationic, anionic, and nonionic surfactants, respectively. To investigate effects of small molecular surfactants on physical stability, turbidimetric, and rheological properties of protein-stabilized Pickering nanoemulsions, various treatments mimicking food processing including pH, heat, freeze-thaw, and salt were applied. Results revealed that the droplet size and polydispersity index of the nanoemulsion prepared with WPI alone were increased after heat treatment or at pH condition near the isoelectric point of WPI, indicating a low physical stability. However, nanoemulsions prepared with WPI-SDS or WPI-CTAB maintained their initial state even after heat treatment including autoclave. Furthermore, there was no significant change in the droplet size of the nanoemulsion prepared with WPI-Tween after freeze-thaw and salt treatments. Although Pickering nanoemulsion stabilized with both WPI and SDS had the highest viscosity, Turbiscan stability index (TSI) was the highest. However, the TSI of the nanoemulsions added with CTAB or Tween 20 was lower than that of the nanoemulsions prepared with WPI alone, confirming that the storage stability of protein-stabilized Pickering nanoemulsion was improved by adding small molecular surfactants.